The present invention relates to storage containers, and more particularly to closure devices for storage containers, such as a door, gate or chute.
Bulk commodity hoppers are storage containers commonly used to store a wide variety of products, such as grain, produce, fertilizer, and rock. Hoppers may be incorporated into trailers, vessels, railroad cars, and other vehicles to transport a bulk commodity, or may be part of a stationary storage structure. Hoppers generally use gravity to discharge the bulk commodity stored within the hopper, and include sloping panels that direct the bulk commodity to a common lower discharge outlet near the bottom of the hopper. In some prior art arrangements, a rigid sliding trap door is used to open, close, or seal the lower discharge outlet. Because the trap door is located under the bulk commodity, the gravitational force from the bulk commodity applies a relatively large downward force upon the trap door. The trap door is generally a horizontally moving door, and the downward force from the commodity on the door creates a friction force against the trap door while the door is being opened.
Prior art trap doors are typically rigid structures with flat upper surfaces, and slide along rails or guides while being opened or closed. As the trap door slides open, the friction from the bulk commodity resists the opening movement and hinders sliding the trap door out from underneath the bulk commodity. Due to the friction force caused by the bulk commodity, a relatively large force may be required to open the trap door. In some prior art trap door opening systems, a gear reduction mechanism provides a mechanical advantage and enables a person to overcome the frictional forces and open the trap door more easily. However, gear reduction mechanisms are often heavy, cumbersome, and can result in slower opening speeds and/or loss of control of the door.
Trap doors of bulk commodity hoppers are usually operated manually with a crank assembly, and the operator must overcome the friction force to open the door. Therefore, any reduction of the friction force also tends to reduce the effort a person must exert to open the door. One known method to reduce the friction force is to have a wedge-shaped door with a slightly inclined top surface so that one end of the door is slightly higher than the other end. An example of a trap door utilizing such an inclined top surface is disclosed in U.S. Pat. No. 6,085,948 issued to Putze. This slanted design slightly shifts the normal force on the door to provide a horizontally acting force component, but the rigid trap door still experiences friction from sliding across the bulk commodity. The force needed to open the slanted trap door may be reduced with this method, but the required force is still relatively large and may be difficult for an average person to operate.
The invention provides a closure device that greatly reduces the force required to open the closure device. The closure device utilizes a belt or flexible membrane for the trap door. The belt rolls or xe2x80x9cpeelsxe2x80x9d away from under the bulk commodity, instead of sliding across it. Since the belt does not slide against the bulk commodity, the friction force between the bulk commodity and the belt is substantially eliminated.
More particularly, the invention has a trap frame that surrounds and defines an aperture near the bottom of the hopper. The trap frame supports a trap door that moves with respect to the trap frame between an open condition and a closed condition. When the trap door is in the open condition, the aperture is open and the bulk commodity may pass through the aperture. When the trap door is in the closed condition, the aperture is closed and substantially sealed, and the bulk commodity may be retained within the hopper.
The trap door includes a traversing frame and a belt. The traversing frame has two side supports that are spaced apart, and have longitudinal axes that are substantially parallel to each other. The traversing frame has multiple inner rollers extending between the side supports. The multiple rollers may rotate with respect to the side supports. The traversing frame extends substantially horizontally and moves substantially horizontally from a position beneath the opening to a position away from the opening.
The belt is a flexible member, similar to a conveyor belt, that at least partially surrounds the traversing frame. The belt seals the aperture when the trap door is closed, so the belt must remain in tension to retain the bulk commodity. Both ends of the belt are preferably stationary and are joined to the trap frame to maintain tension in the belt. The belt moves around the traversing frame as the trap door moves between the open and closed conditions.
More accurately, perhaps, the traversing frame moves horizontally within the interior of the belt. As the traversing frame moves from the closed condition to the open condition, the upper run of the belt travels around the end roller of the traversing frame to the bottom of the traversing frame, at the same time xe2x80x9cpeelingxe2x80x9d away from the upper opening and the material in the hopper. During this movement, the lower run of the belt moves around the opposite end roller of the traversing frame, becoming the upper run in a position offset from the opening. This arrangement is similar to a conveyor belt with the frame moving inside the belt instead of being stationary.